Synthesis of Colloidal Gold Nanocrystals Mediated by Surface Charge

Colloidal nanocrystals have garnered significant attention due to their unique optical, electronic, and catalytic properties. However, colloidal synthesis of clean nanocrystals remains challenging due to the use of reducing agents and surfactants. This study presents a reductant- and surfactant-free strategy to synthesize stable colloidal gold nanocrystals. The reducing process is carried out using flow chemistry on a superhydrophobic surface, where droplets impact the surface, generating surface charge that trigger the reduction of metal ions to metal nanocrystals. The chemical kinetics were established based on the generation and transfer of surface charge on the superhydrophobic surface. The reaction rate was well controlled by regulating the hydrodynamics of droplet impact. The product exhibited stable colloidal properties without the addition of surfactants, which is beneficial for enhancing the sensitivity of surface-enhanced Raman spectroscopy (SERS) application. This surface charge-based reaction is general for noble metal ions and superhydrophobic surfaces. Our design strategy provides a facile approach for synthesizing clean gold nanocrystals with good dispersion.